1. Field of the Invention
The present invention relates to a method and apparatus for controlling the parameters of an arc welding process and displaying such parameters.
2. Description of the Prior Art
Arc welding is a fusion welding process in which the heat to create the weld is obtained from an electric arc generally set up between a workpiece (or base metal to be joined or repaired) and an electrode. The arc plays between the workpiece and the electrode.
In some applications a filler metal in the form of a consumable wire, which may or may not function as the electrode, is used to supply metal to the weld area. The arc may be shielded with an appropriate flux or may be submerged in an inert gas.
Tungsten inert gas ("TIG") welding processes use a nonconsumable tungsten electrode and an inert gas such as argon. A separate filler wire may be used in the TIC process if desired. Metal inert gas ("MIG") welding processes use a consumable electrode i.e., steel, aluminum etc. with an inert gas. In either process, the torch carrying the electrode is moved along the workpiece either manually by an operator or automatically by a machine. The arc or weld voltage and current determine the quantity of heat being applied to the workpiece. The resulting weld is largely determined by the weld heat, the electrode travel speed, the size of the workpiece, and where a filler wire is used, the feed rate of the wire.
The desired or demand weld voltage and current for arc welding torches is supplied by conventional power supplies, for example, of the switching type via analog signals from a controller. The supplies may provide current of one polarity i.e., d.c. or reversing polarity, i.e., a.c. The supplies may be controlled to provide a single level output or a modulated output wherein the current varies from a high to a low level at a preselected pulsing rate, i.e., 100 pulses/sec.
Optimum weld process parameters with acceptable tolerances may be determined for a particular workpiece empirically or by trial and error. However, the actual weld parameters will generally differ to a lesser or greater extent from the desired or demand values due to several factors. For example, the length of the arc gap, i.e., distance from the electrode to the workpiece and the resulting weld heat may change due to irregularities in the surface of the workpiece where the electrode is moved via a machine and/or irregularities in the movement of the electrode by an operator in a manual operation. The speed of the electrode travel may also vary from the desired speed resulting in too much or too little weld heat in a given location.
There is a need to provide the operator with feedback in the form of the actual welding process parameters as well as deviations thereof from the demand values which exceed pre-established tolerances so that a defective or marginal weld can be readily ascertained. One prior art TIG system which provides some feedback information has been distributed by MK Products Inc. of Irvine, Calif., (the assignee of this application) under the model namer Advanced Tube Welder, ("ATW"). The ATW system was designed to form a butt weld between two tubular sections by utilizing a motor drive to move a tungsten electrode around the circumference of the tube ends to be welded. The system included an IBM compatible computer with a monochrome or black and white cathode ray tube or monitor for displaying the demand values for the high and low pulsed welding current, slope current and motor speed in alpha numeric symbols. The display included a bar graph showing the instantaneous values of the actual weld voltage, weld current and motor speed. The tube was divided into preset time periods or levels, for example, with four levels representing one complete pass of the electrode around the tube.
It was difficult for an operator to readily correlate the elapsed time as displayed with a particular location of the electrode relative to the tube in the ATW system. Furthermore, it was often difficult for an operator to correlate the demand and actual values of the displayed weld process parameters. With respect to deviations the ATW system recorded only the first fifteen and the last instances in which each parameter exceeded preset tolerance levels on a strip chart recorder, requiring, as a practical matter that the weld be completed before deviations could be ascertained. Further, the deviations were recorded on an elapsed time basis, versus electrode position on the tube, making it somewhat difficult to correlate a weld parameter deviation with a point on the welded tube.
The computer in the ATW system controller was programmed in an auto procedure generation mode to set the weld voltage, current and motor speed at optimum values for a given diameter and tube wall thickness. However, the values were based on time instead of electrode or weld position in degrees from a starting point. For example, the controller would set the weld current at a certain level for X seconds and then at a different level for Y seconds. Again the correlation of the time with the position of the electrode (or torch) was not readily discernable.
The present invention overcomes to a large extent the above as well as other disadvantages of the prior art.